The present invention relates to curable compositions having high solids and low VOC. These curable compositions are especially useful as coatings and may typically be used as primers, topcoats or as clearcoats and/or basecoats in clearcoat/basecoat compositions. These coating compositions are particularly useful as automotive refinish paint compositions. Most new automotive bumpers and some side panels are constructed from elastomeric plastics which can absorb impact shock and hence sustain body integrity. The high impact and chip resistance of these substrates require coatings having much higher impact resistance than conventional coatings. The present invention is directed to coating compositions which provide coatings having improved impact resistance.
In particular, this invention is directed to a coating composition providing extended pot life and excellent cure and consisting of the combination of (i) at least one imine having the structure 
wherein n is 0 to 30, R1 and R2 are selected from the group consisting of hydrogen, alkyl, aryl, cycloaliphatic, and substituted alkyl, aryl, and cycloaliphatic groups; and R1 and R2 may be the same or different; and R3 is selected from the group consisting of aliphatic, aromatic, arylaliphatic, and cycloaliphatic groups and which may also contain O, N, S, or Si; (ii) a polyisocyanate having an average of at least two isocyanate groups per molecule; (iii) at least one polyaspartic ester; (iv) an isocyanate functional urethane; wherein (ii) is different than (iv) and wherein the coating composition is substantially free of hydroxyl functionality.
Two-component curable mixtures comprising polyisocyanates and active hydrogen-containing compounds, such as polyols or polyamines, are well-known in the art to provide excellent performance and cure at low temperatures. However, due to the reactivity of the isocyanates and the active hydrogen-containing compounds, it is often difficult to obtain long pot-lives of the mixture of polyisocyanate and active hydrogen-containing material and yet still enjoy the benefits of rapid cure. This is especially true for low VOC materials, which will incorporate relatively low levels of solvent and will frequently involve low molecular weight, but highly reactive, starting materials.
Accordingly, it is an object of the present invention to provide a two component coating composition having extended pot-life and excellent cure. It is a further object of the present invention to provide an ambient cured coating composition having low VOC and relatively low viscosity. It is an even further object of the present invention to provide an ambient cured coating composition capable of providing a sufficiently flexible coating for curved or flexible substrates.
The present invention relates to a novel coating composition. The coating composition comprises:
(i) an imine having the structure 
wherein n is 0 to 30,
R1 and R2 are selected from the group consisting of hydrogen, alkyl, aryl, cycloaliphatic, and substituted alkyl, aryl, and cycloaliphatic groups; and R1 and
R2 may be the same or different; and
R3 is selected from the group consisting of aliphatic, aromatic, arylaliphatic, and cycloaliphatic groups and which may also contain O, N, S, or Si;
(ii) a polyisocyanate having an average of at least two isocyanate groups per molecule;
(iii) at least one polyaspartic ester;
(iv) an isocyanate functional urethane; and
wherein (ii) is different from (iv) and the coating composition is substantially free of hydroxyl groups. The isocyanate functional urethane comprises the reaction product of:
(a) an aliphatic polyisocyanate having an average of at least 2.1 isocyanate groups per molecule and selected from the group consisting of the biurets and isocyanurates of linear aliphatic diisocyanates; and
(b) at least one monofunctional alcohol having a molecular weight less than about 500 and which is selected from the group consisting of: 
xe2x80x83wherein n is from 1 to about 10; R1 is an aliphatic radical of 1 to about 12 carbons; R2 is H or CH3; R3 and R4 are independently aliphatic of 1 to about 12 carbons or H; R5 is an aliphatic radical of 1 to about 8 carbons or nothing; X is 
xe2x80x83and R6 is an aliphatic radical of 1 to about 12 carbons, and
(c) at least one diol having the formula: 
xe2x80x83wherein R7 is H or CH3 and y is from 1 to about 40; wherein the total NCO/OH equivalents ratio is greater than 1.0 and the ratio or OH equivalents from (b) to OH equivalents from (c) ranges from 0.3:1 to 2.0:1.0.